The Taff’s Well Sewer project in Wales saw contractor Amec Specialist Business construct a 1.6km long, 1.45m o.d. tunnel for the client, Welsh Water, through a truly challenging and extremely varying geology. To deal with the sandstone boulders, of up to 2m3 that were to occupy an estimated 30% of the excavation diameter, and a high silt level, the contractor decided to utilise an Iseki "Super" Unclemole, thought to be the first purchased in Europe. Amec decided on the use of slurry support at the face in combination with an earth pressure balance capability. The drive was split into eight lengths that were bored at an average depth of 13m from eight 6m diameter shafts. A serious challenge to the project was not only the crossing of a railway line, but having to twice cross a main road, at one point passing just 3m below the 800mm Cardiff freshwater main. Amec completed the project successfully by combining a wealth of experience with an innovate approach to microtunnelling and choice of machine.
Judging Panel’s Comments: The award goes to a project which, on the face of it, is tunnelled through ground at the limit of no dig technology. Limited cover, water bearing sands and gravels, dense clay and extensive large pennant sandstone boulders were only some of the obstacles that faced this particular contract. With no alternative to the no-dig approach, the contractor has demonstrated considerable skills in machine and slurry development, achieving a timely and cost effective conclusion.
